feat(ci): add workflow for publishing packages

.github/workflows/packaging.yml

@@ -5,8 +5,12 @@ name: Packaging
 # identical to the canonical copies at the repository root.
 # Build backends stay silent when those files go missing, so the artifacts are
 # inspected explicitly.
+#
+# Also called by release.yml, which publishes the core distributions from the
+# uploaded "dist" artifact.
 
 on:
+  workflow_call:
   workflow_dispatch:
   push:
     branches: [main]
@@ -19,6 +23,7 @@ on:
       - "examples/*/third-party-programs.txt"
       - ".github/scripts/check_dist_licenses.py"
       - ".github/workflows/packaging.yml"
+      - ".github/workflows/release.yml"
   pull_request:
     paths: *packaging-paths
 
@@ -42,11 +47,13 @@ jobs:
         with:
           # The core package version is derived from the git history.
           fetch-depth: 0
+          persist-credentials: false
 
       - name: Set up Python
         uses: actions/setup-python@6d4fd22b20465ccc0f7354476588e8df7c9ca0e0 # v7.1.0
         with:
-          python-version: "3.x"
+          # Keeping this pinned, so we have stable release environment
+          python-version: "3.14"
 
       - name: Set up uv
         uses: astral-sh/setup-uv@07a047e608db84b3d8c06cd9a7c7dcc9c355c18e # v10.3.2
@@ -73,3 +80,10 @@ jobs:
 
       - name: Verify license files in all distributions
         run: python3 .github/scripts/check_dist_licenses.py dist/core/* dist/examples/*.whl
+
+      - name: Upload core distributions
+        uses: actions/upload-artifact@cf430e030ddbb5b0abf93d22962f4752f3646cd9 # v7.0.2
+        with:
+          name: dist
+          path: dist/core/
+          if-no-files-found: error

.github/workflows/release.yml

@@ -0,0 +1,114 @@
+name: Release
+
+# Publishes the torch-tweak core distributions to PyPI and TestPyPI.
+#
+# Only release tags are allowed, e.g. v0.5.0 or v0.5.0rc1.
+#
+on:
+  workflow_dispatch:
+    inputs:
+      target:
+        description: Package index to publish to
+        type: choice
+        options:
+          - testpypi
+          - pypi
+        default: testpypi
+
+# Never cancel a release midway: a partial upload cannot be redone with the
+# same version.
+concurrency:
+  group: release
+  cancel-in-progress: false
+
+permissions:
+  contents: read
+
+jobs:
+  validate-tag:
+    name: Validate release tag
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Require a tagged commit
+        env:
+          REF_TYPE: ${{ github.ref_type }}
+          REF_NAME: ${{ github.ref_name }}
+        run: |
+          if [ "${REF_TYPE}" != "tag" ]; then
+            echo "::error::Run this workflow on a release tag."
+            exit 1
+          fi
+          if ! printf '%s' "${REF_NAME}" | grep -Eq '^v[0-9]+\.[0-9]+\.[0-9]+(rc[0-9]+)?$'; then
+            echo "::error::Tag '${REF_NAME}' does not match vX.Y.Z or vX.Y.ZrcN."
+            exit 1
+          fi
+
+      - name: Checkout Torch Tweak repository
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        with:
+          fetch-depth: 0
+          persist-credentials: false
+
+      - name: Require the tagged commit to be on main
+        env:
+          REF_NAME: ${{ github.ref_name }}
+        run: |
+          if ! git merge-base --is-ancestor "${GITHUB_SHA}" origin/main; then
+            echo "::error::Tag '${REF_NAME}' points to ${GITHUB_SHA}, which is not on main."
+            exit 1
+          fi
+
+  # Note: packaging.yml also builds the example wheels, which are never
+  # published, so a broken example blocks the release.
+  build:
+    name: Build
+    needs: validate-tag
+    uses: $/.github/workflows/packaging.yml
+
+  publish:
+    name: Publish to ${{ inputs.target }}
+    needs: build
+    runs-on: ubuntu-latest
+    environment:
+      name: ${{ inputs.target }}
+      url: >-
+        ${{ inputs.target == 'pypi'
+          && format('https://pypi.org/project/torch-tweak/{0}/', steps.version.outputs.version)
+          || format('https://test.pypi.org/project/torch-tweak/{0}/', steps.version.outputs.version) }}
+    permissions:
+      id-token: write # PyPI trusted publishing (OIDC) and attestation signing
+
+    steps:
+      - name: Download distributions
+        uses: actions/download-artifact@9000827ccba6bdab643e8b6fd33ac0654aef8333 # v8.0.2
+        with:
+          name: dist
+          path: dist/core/
+
+      - name: Require the built version to match the tag
+        id: version
+        env:
+          REF_NAME: ${{ github.ref_name }}
+        run: |
+          version="${REF_NAME#v}"
+          expected="$(printf '%s\n' \
+            "torch_tweak-${version}-py3-none-any.whl" \
+            "torch_tweak-${version}.tar.gz" | sort)"
+          actual="$(ls dist/core | sort)"
+          if [ "${actual}" != "${expected}" ]; then
+            echo "::error::dist/core does not match version ${version}."
+            printf 'Expected:\n%s\nActual:\n%s\n' "${expected}" "${actual}"
+            exit 1
+          fi
+          echo "version=${version}" >> "${GITHUB_OUTPUT}"
+
+      - name: Publish to ${{ inputs.target }}
+        uses: pypa/gh-action-pypi-publish@7245906fb61fa33a13554f9d5fb856fe61758086 # v1.14.3
+        with:
+          attestations: true
+          packages-dir: dist/core/
+          repository-url: >-
+            ${{ inputs.target == 'pypi'
+              && 'https://upload.pypi.org/legacy/'
+              || 'https://test.pypi.org/legacy/' }}